On 12/27/2010 03:36 PM, ahmet erkan wrote:
>"I did try using a GFCI on the engine room circuit but the
environment in the ER was too damp and it wouldn't hold.
>I have not tried it elsewhere but I don't know why they wouldn't work.
>Even though the neutral is floating (on my boat), all the non-current
carrying metal parts are still grounded."
With a "floating Neutral", the GFCI is going to detect a current
from hot terminal through a person to earth and trip
open only if the neutral insulation has also broken down to ground,
similarly GFCI is going to detect a current from
neutral through a person to earth and open only if the hot line
insulation has also broken down to earth. (I believe
Norm has also said this in different words)
If one wants to use GFCI devices with a floating Neutral, I suggest
he/she (so PC) connects a 1uF capacitor from the
hot line to ship's ground and another 1uF capacitor from the neutral
to the ships ground.
Both capacitors should be connected to the line side of the GFCI
device. (ie: at the 120V secondary of your shielded
isolation transformer preferably close to the transformer for noise
attenuation purposes)
"60V is safer than 120V" in fact the 48V used by the phone company is
actually the terminal voltage of a
48V rated battery that is typically at 55V and could go to 60V during
equalize. At the phone company we routinely
worked on the 48V live equipment and touched the negative
terminal (positive terminal is grounded for galvanic
corrosion prevention) without worrying about getting electrocuted.
So there you are, a +/-60Vac ships system with a GFCI protection
device that will trip if there is more than 5mA
imbalance between the hot or neutral currents and a little safer than
your floating Neutral system. The imbalance
will occur and interrupt the circuit either during a "heavy wet
contact" by the user or if there is a fault in the system.
The GFCI used in a grounded neutral system cannot detect Neutral
to Ground type ground faults reliably
due to lack of a supply to drive the current but the +/- 60V system
_should_ detect either Hot to ground or Neutral
to ground insulation failures equally reliably. (Do test anyway)
The capacitors should also work in tandem with the shield during
lightning storms and provide common mode
attenuation to voltage spikes in the order of 120dB. The capacitors
should also work in tandem with the leakage
inductance of the isolation transformer and provide normal mode
attenuation to voltage spikes proportional to
frequency of the disturbance.
Again, test for proper functionality of any system before relying on
it for safety.
This method of wiring is just a paper design at this time and has not
been verified, I can verify using my isolation
transformer and a GFCI receptacle or a CB from Home Depot and provide
the results to the list if anyone wants
to implement it?
BTW who is Dr. Oz? A friend of George Orwell? I learn so many things
on this list.
Fair winds
S/V 8827
Ahmet
------------------------------------------------------------------------
From: banders...@earthlink.net
To: liveaboard@liveaboardonline.com
Date: Sat, 25 Dec 2010 17:13:30 -0500
Subject: Re: [Liveaboard] GALVANIC ISOLATOR
See Annotations Below
Norm
S/V Bandersnatch
Lying Julington Creek FL
N30 07.68 W081 38.47
----- Original Message -----
*From:* ahmet erkan <mailto:ameter...@hotmail.com>
*To: *liveabo...@liveaboardonline.com
<mailto:liveaboard@liveaboardonline.com>
*Sent:* 12/20/2010 11:04:05 PM
*Subject:* Re: [Liveaboard] GALVANIC ISOLATOR
Hi Norm,
I am not sure if your questions have already been answered by the
list but let me make an attempt anyway.
You asked :
_"would you please address the issue of connecting (or not
connecting) the ac neutral to earth."_
IMO not connecting the ac neutral to earth would make
the electrical system safe for the user making accidental contact
with a hot conductor. However if the user begins to ignore the
basic safety rules and becomes complacent about touching hot
conductors he/she will be at the mercy of the system being fault
free. Therefore a system with an isolated neutral ought to be
checked frequently (preferably automatically) to verify all the
current carrying conductors are indeed isolated from the chassis.
Another shortcoming of the ungrounded neutral is you cannot use
GFCI circuit breakers.
One other shortcoming may be the increased vulnerability of your
electronics to lightning! . The isolation transformer that is
providing the floating secondary neutral should be shielded
(preferably both primary and secondary shields) and the shields
should be hardwired to earth.
Norm - Yes, I agree (and stated) that a way to check for ground
faults would be a Good Thing. Even a simple light bulb or meter.
There is a shield on my isolation transformer between the windings
and it is grounded to ship's ground.
I did try using a GFCI on the engine room circuit but the
environment in the ER was too damp and it wouldn't hold. I have
not tried it elsewhere but I don't know why they wouldn't work.
Even though the neutral is floating (on my boat), all the
non-current carrying metal parts are still grounded.
From what I understand about lightening damage it is small
voltages inside sensitive electronics induced by the nearby heavy
current flows from lightening that does the most damage.
You asked :
_"I believe in the US power that comes into a house is from a
center tapped secondary winding in the pole transformer which
delivers 240 vac at the ends of the coil and the neutral comes
from the center tap. The grounding of the neutral is only added
in the house's breaker box by the neutral/grounding jumper wire.
Correct me if I am mistaken."_
Correct, except I have never seen a jumper wire. The
panels usually have a long aluminum block bolted to the chassis
and it has a bunch of screw terminals for both neutral and ground
wires. US house wiring code requires both neutral (white) and
ground (green) wires to be terminated to the chassis of the
distribution panel/circuit breaker box. The chassis of the
distribution panel is also routed (with a green wire) to a ground
rod or a buried water pipe. I remember some Canadian folks on the
list freaking out when they heard white neutral and green ground
wires are bonded at the chassis of the panel but this is the way
it is, and it makes sense to us.
Norm - My memory (such as it is) tells me that the neutral
terminal block in the US is insulated, the grounding block not
insulated, and there is a wire connecting the two. But I have
made a note on my "To Do" list to have a look in a breaker box the
next time I am in Lowes or Home Depot.
You asked :
_"I seem to have read that the European electrical system has
ungrounded neutrals. Is this true or not?"
_In Turkey the houses are wired to one phase of the 220V Wye pole
transformers with a pair of copper wires. One wire is hot and it
has insulation, the other wire is the neutral and it is a bare
copper conductor. The bare wire is bonded to the steel pipes that
bring water to the house. The metal surfaces of the appliances are
bonded to the bare neutral with a jumper and this jumper may be
opened by the electrician to test the appliance for leakage. I
believe the newer houses are using an insulated neutral and a bare
ground wire so that GFCI devices can be used. The chassis to
neutral jumper on the appliances are removed to be able to use the
GFCI devices in bathrooms.
Cheers
Ahmet
Norm - Thank you for the great information about how it is done in
Turkey. It sounds safe to me and I'd bet Dr. Oz would approve it too.
http://www.doctoroz.com/
Dr Oz has a USA TV program and gives medical advice. He's rather
popular these days.
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